Variable rate transmission and reception methods, and variable rate transmission and reception devices

ABSTRACT

A transmission method for implementing variable rate transmission. Part of the baseband processing of a transmitter based on a CDMA transmission scheme is described. A transmitted information sequence in the form of a digital signal is phase modulated by a phase modulator  105.  An orthogonal code generator  101  selects, in response to rate information of the transmitted signal, the orthogonal code to be generated. The bit rate of the orthogonal code the orthogonal code generator  101  generates is double the maximum transmission rate. The modulated transmitted signal is multiplied by the orthogonal code corresponding to the rate information with a multiplier  103.  The transmitted signal, which is multiplied by the orthogonal code corresponding to the rate information, is further multiplied by a spreading code sequence with a multiplier  104  to be spread into a CDMA signal, and is transmitted under power transmission control based on the rate information. A receiving side can detect the rate without information about the transmission rate.

TECHNICAL FIELD

[0001] The present invention relates to a variable rate transmissionmethod in radio communications, and more particularly to a variable ratetransmission method and equipment for implementing it, which areapplicable to direct spreading code division multiple access (DS-CDMA)in mobile communications.

BACKGROUND ART

[0002] In DS-CDMA, information data undergoes narrow-band carriermodulation (such as binary phase shift keying or quadrature phase shiftkeying), followed by spreading using a higher rate binary spreading codesequence, and by transmission. On a receiving side, the received signalis-multiplied by the same binary spreading code sequence as that used inthe transmission to acquire the original narrow-band modulated signal,followed by demodulation to the original transmitted data.

[0003] In actual communications, however, the information rate is notalways kept constant. For example, although voice communications iscarried out at a rate of about 8 kbps, pauses in which no voice signalis present takes place frequently, and lowering the information rate inthe pauses little degrades the voice quality. It is very important forthe CDMA to reduce transmission power during a low information rate tominimize interference on other channels.

[0004] This is because the magnitude of interference determines thecommunication quality. Thus, implementation of the variable ratetransmission method is important in the CDMA.

[0005] As one of the variable rate methods, intermittent transmission isknown. It carries out, during a maximum information rate, continuoustransmission, but reduces, at lower rates, the average transmission ratedown to an information rate by decreasing the ratio of transmissionintervals with maintaining the instantaneous transmission rate at themaximum, thereby trying to reduce the interference amount.

[0006] As for the intermittent transmission, refer to the followingliterature.

[0007] Reference 1: R. Padovani, R., “Reverse link performance of IS-95based cellular systems”, IEEE Personal Communications, pp. 28-34, 3rdQuarter, 1994.

[0008] Reference 2: Y. Okumura and F. Adachi, “Variable rate datatransmission with blind rate detection for coherent DS-CDMA mobileradio”, IEE Electron Lett. vol. 32, pp. 1865-1866, September 1996.

[0009] As another variable rate transmission method in the CDMA,continuous transmission is known which not only varies the instantaneoustransmission rate of radio in response to variations in the informationrate, but also controls the transmission power in response to thetransmission rate.

[0010] The average interference amount can also be reduced in thecontinuous transmission as in the intermittent transmission because thetransmission power is varied (in inverse proportion to) the transmissionrate in the continuous transmission.

[0011] In the CDMA technology, the transmission power control isessential which controls the transmission power so that a received SIR(signal to interference ratio) measured on the receiving side matches apredetermined target SIR in response to results obtained by comparingthe two values (refer to Japanese patent application laid-open No.8-162972/1996 applied by the assignee of the present invention, forexample). In this technique, the SIR of a received signal is measuredslot by slot and compared with the target SIR, the slot being defined asa section in a received signal sandwiched by two successive pilotsignals of a known pattern which are transmitted periodically. Then, atransmission control command is generated in response to the comparedresult, and is transmitted to the transmitting side to be reflected onthe transmission power control. The transmission period of thetransmission power control command is a slot interval, that is, themeasuring interval.

[0012] The transmission power control cannot maintain constant receptionquality if it uses the same target SIR for different rates when varyingthe transmission power in response to the transmission rate. Therefore,the conventional transmission power control that employs the target SIRcannot be applied without change to a transmitted signal whosetransmission power is controlled in response to the transmission rate.

DISCLOSURE OF THE INVENTION

[0013] An object of the present invention is to provide a transmittingmethod and receiving method and equipment for implementing the variablerate transmission method employing the foregoing continuous transmissionscheme.

[0014] Another object of the present invention is to implement thetransmission power control capable of achieving constant receivingquality on the receiving side regardless of rate variations when thetransmission power is varied in response to the transmission rate (ininverse proportion to it, for example).

[0015] In order to accomplish the objects aforementioned, according tothe invention as claimed in claim 1, a variable rate transmission methodcomprises the steps of:

[0016] selecting, in accordance with a rate of information to betransmitted, one of a plurality of orthogonal codes whose length differsfrom each other and whose information rate is at least twice a maximuminformation rate; and

[0017] multiplying a transmitted signal by the selected orthogonal code.

[0018] According to the invention as claimed in claim 2, in the variablerate transmission method as claimed in claim 1, the orthogonal code isobtained by successively generating, using lower degree matrices under apredetermined rule, higher degree (2^(N)×2^(N) elements, where N is aninteger equal to or greater than one) matrices with their row vectorsorthogonal to each other, and by selecting one of row vectors of one ofthe matrices with a degree varying in accordance with a peaktransmission rate of transmitted data.

[0019] According to the invention as claimed in claim 3, in the variablerate transmission method as claimed in claim 2, the orthogonal code isselected, when selecting one of row vectors of a 2^(k)×2^(k) elementmatrix, where k is an integer less than N, such that any of row vectorswhich belong to any one of 2^(j)×2^(j) element matrices, where j is aninteger greater than k, and which are already assigned as the orthogonalcodes, do not include as their sub-vector, a row vector to be selectedand a row vector obtained by inverting the row vector to be selected.

[0020] According to the invention as claimed in claim 4, in the variablerate transmission method as claimed in any one of claims 1-3, thetransmitted signal is further multiplied by a spreading code sequence tobe spectrum spread, and is transmitted at transmission powercorresponding to the rate.

[0021] According to the invention as claimed in claim 5, the variablerate transmission method as claimed in claim 4, further comprises thesteps of:

[0022] inserting pilot symbols of a known pattern periodically into datasymbols corresponding to the information to be transmitted; and

[0023] varying the rate on a frame by frame basis, the frame consistingof a plurality of slots defined by the pilot symbols.

[0024] According to the invention as claimed in claim 6, the variablerate transmission method as claimed in claim 5, further comprises thestep of controlling the transmission power on a slot by slot basis inresponse to a transmission power control command sent from a receivingside.

[0025] According to the invention as claimed in claim 7, the variablerate transmission method as claimed in claim 6, further comprises thestep of transmitting, in a slot immediately after a rate change, thepilot symbols at power corresponding to the rate before the rate change.

[0026] According to the invention as claimed in claim 8, the variablerate transmission method as claimed in claim 6, further comprises thestep of suspending the transmission power control by the transmissionpower control command that is associated with at least one of slotsimmediately after a rate change.

[0027] According to the invention as claimed in claim 9, in the variablerate transmission method as claimed in claim 8, a number of slots withwhich the transmission power control is suspended is determined inresponse to transmission quality.

[0028] According to the invention as claimed in claim 10, in thevariable rate transmission method as claimed in any one of claims 6-8,the pilot symbols are transmitted at a same rate as that of the frame.

[0029] According to the invention as claimed in claim 11, in thevariable rate transmission method as claimed in any one of claims 6-8,the pilot symbols are transmitted at a fixed rate.

[0030] According to the invention as claimed in claim 12, a variablerate receiving method for receiving a signal transmitted by the variablerate transmission method as claimed in any one of claims 1-5 comprisesthe steps of:

[0031] generating a sampled sequence of a received signal by samplingthe received signal at a rate of one of the orthogonal codes, andcalculating correlations between the sampled sequence of the receivedsignal and the plurality of orthogonal codes with different lengths;

[0032] deciding an orthogonal code that gives a maximum correlation bycomparing correlation values obtained as a result of the calculation ofthe correlations; and

[0033] demodulating the received signal by multiplying the sampledsequence of the received signal by the orthogonal code that gives themaximum correlation value.

[0034] According to the invention as claimed in claim 13, a receivingmethod for receiving a signal transmitted by the variable ratetransmission method as claimed in any one of claims 6-8 comprises thesteps of:

[0035] generating a sampled sequence of a received signal by samplingthe received signal at a rate of one of the orthogonal codes;

[0036] calculating correlations between the sampled sequence of thereceived signal and the plurality of orthogonal codes with differentlengths;

[0037] deciding an orthogonal code that gives a maximum correlation bycomparing correlation values obtained as a result of the calculation ofthe correlations;

[0038] demodulating the received signal by multiplying the sampledsequence of the received signal by the orthogonal code that gives themaximum correlation value, and measuring a received SIR for each slot ofthe received signal;

[0039] correcting the received SIR according to a rate of the orthogonalcode decided by the step of deciding;

[0040] comparing the corrected received SIR with a target SIR; and

[0041] generating a transmission power control command in response to aresult of the comparing.

[0042] According to the invention as claimed in claim 14, in thereceiving method as claimed in claim 13, demodulation of the receivedsignal is carried out slot by slot.

[0043] According to the invention as claimed in claim 15, a receivingmethod for receiving a signal transmitted by the variable ratetransmission method as claimed in claim 7 comprises the steps of:

[0044] generating a sampled sequence of a received signal by samplingthe received signal at a rate of one of the orthogonal codes;

[0045] calculating correlations between the sampled sequence of thereceived signal and the plurality of orthogonal codes with differentlengths;

[0046] deciding an orthogonal code that gives a maximum correlation bycomparing correlation values obtained as a result of the calculation ofthe correlations;

[0047] demodulating the received signal by multiplying the sampledsequence of the received signal by the orthogonal code that gives themaximum correlation value;

[0048] measuring a received SIR of the pilot symbols for a slotimmediately after a rate change, and a received SIR for each of otherslots;

[0049] correcting the received SIR for each of other slots according toa rate decided by the decision of the orthogonal code;

[0050] correcting the received SIR of the pilot symbols according to arate before the rate change;

[0051] comparing the corrected received SIR with a target SIR; and

[0052] generating a transmission power control command in response to aresult of the comparing.

[0053] According to the invention as claimed in claim 16, a receivingmethod for receiving a signal transmitted by the variable ratetransmission method as claimed in claim 9 comprises the steps of:

[0054] generating a sampled sequence of a received signal by samplingthe received signal at a rate of one of the orthogonal codes;

[0055] calculating correlations between the sampled sequence of thereceived signal and the plurality of orthogonal codes with differentlengths;

[0056] deciding an orthogonal code that gives a maximum correlation bycomparing correlation values obtained as a result of the calculation ofthe correlations;

[0057] demodulating the received signal by multiplying the sampledsequence of the received signal by the orthogonal code that gives themaximum correlation value;

[0058] measuring a received SIR of the pilot symbols at the fixed rate;

[0059] correcting the received SIR according to a rate decided by thedecision of the orthogonal code;

[0060] comparing the corrected received SIR with a target SIR; and

[0061] generating a transmission power control command in response to aresult of the comparing.

[0062] According to the invention as claimed in claim 17, a variablerate transmitter comprises:

[0063] an orthogonal code generator for generating, in accordance with arate of information to be transmitted, one of a plurality of orthogonalcodes whose length differs from each other and whose information rate isat least twice a maximum information rate; and

[0064] a multiplier for multiplying a transmitted signal by theorthogonal code fed from the orthogonal code generator.

[0065] According to the invention as claimed in claim 18, in thevariable rate transmitter as claimed in claim 17, the orthogonal code isobtained by successively generating, using lower degree matrices under apredetermined rule, higher degree (2^(N)×2^(N) elements, where N is aninteger equal to or greater than one) matrices with their row vectorsorthogonal to each other, and by selecting one of row vectors of one ofthe matrices with a degree varying in accordance with a peaktransmission rate of transmitted data.

[0066] According to the invention as claimed in claim 19, in thevariable rate transmitter as claimed in claim 18, the orthogonal code isselected, when selecting one of row vectors of a 2^(k)×2^(k) elementmatrix, where k is an integer less than N, such that any of row vectorswhich belong to any one of 2^(j)×2^(j) element matrices, where j is aninteger greater than k, and which are already assigned as the orthogonalcodes, do not include as their sub-vector, a row vector to be selectedand a row vector obtained by inverting the row vector to be selected.

[0067] According to the invention as claimed in claim 20, the variablerate transmitter as claimed in any one of claims 17-19, furthercomprises:

[0068] a spreading sequence generator for generating a spreading codesequence for spectrum spreading;

[0069] a multiplier for multiplying the transmitted signal by thespreading code sequence fed from the spreading sequence generator; and

[0070] a transmitter for varying transmission power in response to thetransmission rate.

[0071] According to the invention as claimed in claim 21, the variablerate transmitter as claimed in claim 20, further comprises a pilotsymbol generator for generating pilot symbols of a known patternperiodically, wherein the pilot symbols are inserted into data symbolscorresponding to the information to be transmitted, and the rate isvaried on a frame by frame basis, the frame consisting of a plurality ofslots defined by the pilot symbols.

[0072] According to the invention as claimed in claim 22, the variablerate transmitter as claimed in claim 21, further comprises atransmission power controller for controlling the transmission power ona slot by slot basis in response to a transmission power control commandsent from a receiving side.

[0073] According to the invention as claimed in claim 23, in thevariable rate transmitter as claimed in claim 22, the pilot symbols aretransmitted, in a slot immediately after a rate change, at powercorresponding to the rate before the rate change.

[0074] According to the invention as claimed in claim 24, in thevariable rate transmitter as claimed in claim 21, where the pilotsymbols are transmitted at a same rate as that of the frame.

[0075] According to the invention as claimed in claim 25, in thevariable rate transmitter as claimed in claim 21, where the pilotsymbols are transmitted at a fixed rate.

[0076] According to the invention as claimed in claim 26, in thevariable rate transmitter as claimed in claim 22, the transmission powercontrol by the transmission power control command that is associatedwith at least one of slots immediately after a rate change is suspended.

[0077] According to the invention as claimed in claim 27, in thevariable rate transmitter as claimed in claim 26, a number of slots withwhich the transmission power control is suspended is determined inresponse to transmission quality.

[0078] According to the invention as claimed in claim 28, a variablerate receiver for receiving a signal transmitted by the variable ratetransmission method as claimed in any one of claims 1-5 comprises:

[0079] a sampler for generating a sampled sequence of a received signalby sampling the received signal at a rate of one of the orthogonalcodes;

[0080] a correlator for calculating correlations between the sampledsequence of the received signal from the sampler and the plurality oforthogonal codes with different lengths;

[0081] an orthogonal code decision block for deciding an orthogonal codethat gives a maximum correlation by comparing correlation valuesobtained as a result of the calculation of the correlations;

[0082] an orthogonal code generator for generating the orthogonal codedecided by the orthogonal code decision block; and

[0083] a multiplier for multiplying the sampled sequence of the receivedsignal by the orthogonal code from the orthogonal code generator todemodulate the received signal.

[0084] According to the invention as claimed in claim 29, a receiver forreceiving a signal transmitted by the variable rate transmission methodas claimed in any one of claims 6-8 comprises:

[0085] a sampler for generating a sampled sequence of a received signalby sampling the received signal at a rate of one of the orthogonalcodes;

[0086] a correlator for calculating correlations between the sampledsequence of the received signal and the plurality of orthogonal codeswith different lengths;

[0087] an orthogonal code decision block for deciding an orthogonal codethat gives a maximum correlation by comparing correlation valuesobtained as a result of the calculation of the correlations;

[0088] an orthogonal code generator for generating the orthogonal codedecided by the orthogonal code decision block;

[0089] a multiplier for multiplying the sampled sequence of the receivedsignal by the orthogonal code from the orthogonal code generator;

[0090] a received SIR for measuring a received SIR for each slot of thereceived signal;

[0091] a correcting block for correcting the received SIR according to arate of the orthogonal code decided; and

[0092] a comparator for comparing the corrected received SIR with atarget SIR,

[0093] wherein a transmission power control command is generated inresponse to a result of the comparing.

[0094] According to the invention as claimed in claim 30, in thereceiver as claimed in claim 29, demodulation of the received signal iscarried out slot by slot.

[0095] According to the invention as claimed in claim 31, a receiver forreceiving a signal transmitted by the variable rate transmission methodas claimed in claim 7 comprises:

[0096] a sampler for generating a sampled sequence of a received signalby sampling the received signal at a rate of one of the orthogonalcodes;

[0097] a correlator for calculating correlations between the sampledsequence of the received signal from the sampler and the plurality oforthogonal codes with different lengths;

[0098] an orthogonal code decision block for deciding an orthogonal codethat gives a maximum correlation by comparing correlation valuesobtained as a result of the calculation of the correlations;

[0099] an orthogonal code generator for generating the orthogonal codedecided by the orthogonal code decision block;

[0100] a multiplier for multiplying the sampled sequence of the receivedsignal by the orthogonal code from the orthogonal code generator;

[0101] a received SIR measuring block for measuring a received SIR ofthe pilot symbols for a slot immediately after a rate change, and areceived SIR for each of other slots;

[0102] a correcting block for correcting the received SIR for each ofother slots according to a rate decided by the decision of theorthogonal code, and for correcting the received SIR of the pilotsymbols according to a rate before the rate change; and

[0103] a comparator for comparing the corrected received SIR with atarget SIR,

[0104] wherein a transmission power control command is generated inresponse to a result of the comparing.

[0105] According to the invention as claimed in claim 32, a receiver forreceiving a signal transmitted by the variable rate transmission methodas claimed in claim 11 comprises:

[0106] a sampler for generating a sampled sequence of a received signalby sampling the received signal at a rate of one of the orthogonalcodes;

[0107] a correlator for calculating correlations between the sampledsequence of the received signal and the plurality of orthogonal codeswith different lengths;

[0108] an orthogonal code decision block for deciding an orthogonal codethat gives a maximum correlation by comparing correlation valuesobtained as a result of the calculation of the correlations;

[0109] a multiplier for multiplying the sampled sequence of the receivedsignal by the orthogonal code that gives the maximum correlation value;

[0110] a received SIR measuring block for measuring a received SIR ofthe pilot symbols at the fixed rate;

[0111] a correcting block for correcting the received SIR according to arate decided by the decision of the orthogonal code; and

[0112] a comparator for comparing the corrected received SIR with atarget SIR,

[0113] wherein a transmission power control command is generated inresponse to a result of the comparing.

BRIEF DESCRIPTION OF THE DRAWINGS

[0114]FIG. 1 is a block diagram of a transmitter;

[0115]FIG. 2 is a table illustrating a generating scheme of orthogonalcode sequences;

[0116]FIG. 3 is a graph illustrating a structure of the orthogonal codesequences;

[0117]FIG. 4 is a graph illustrating orthogonal code sequences to beused;

[0118]FIGS. 5A and 5B are graphs each illustrating other orthogonal codesequences to be used;

[0119]FIG. 6 is a block diagram showing a receiver;

[0120]FIG. 7 is a block diagram showing a portion of the receiver, whichmeasures the received SIR of a received signal; and

[0121]FIG. 8 is a diagram illustrating the operation of the receiver.

BEST MODE FOR CARRYING OUT THE INVENTION

[0122] The invention will now be described with reference to theaccompanying drawings.

[0123]FIG. 1 is a block diagram showing an embodiment in accordance withthe present invention, which illustrates part of a baseband processingin a transmitter based on the CDMA transmission scheme. In FIG. 1, thereference numeral 105 designates a phase modulator for performing phasemodulation of a transmitted information sequence in the form of adigital signal. The reference numeral 103 designates a multiplier formultiplying the phase modulated transmitted signal by an orthogonal codegenerated by an orthogonal code generator 101 in response to atransmission rate. The multiplied transmitted signal is furthermultiplied in a multiplier 104 by a spreading code sequence fed from aspreading code sequence generator 102, thereby being spread.

[0124] The orthogonal code generator 101 selects its generatingorthogonal code in accordance with the rate information of thetransmitted signal. The bit rate of the orthogonal code generated by theorthogonal code generator 101 is double the maximum transmission rate.

[0125] The multiplier 103 multiplies the modulated transmitted signal bythe orthogonal code corresponding to the rate information. Thetransmitted signal multiplied by the orthogonal code corresponding tothe rate information is further multiplied by the spreading codesequence with the multiplier 104 to be spectrum spread into a CDMAsignal which is transmitted under the transmission power control inresponse to the rate information.

[0126] In FIG. 1, the orthogonal code employed by the transmissionmethod when the information rate is 1/Q of the maximum rate is asequence of a total of 2Q binary codes consisting of Q consecutive 1sand Q consecutive −1s, for example. Since the duration of the orthogonalcode equals one information length, the bit rate of the orthogonal codeis always double the maximum information rate. The orthogonal codegenerated by the orthogonal code generator 101 will now be described indetail.

[0127] The orthogonal code produced by the orthogonal code generator 101is generated according to a certain rule as shown in FIG. 2. In FIG. 2,a matrix C₂ consists of row vectors C₂ (1)=(1,1) and C₂(2)=(1,−1).{overscore (C)}₂(1) and {overscore (C)}₂(2) represent row vectors inwhich 1 and −1 in C₂(1) and C₂(2) are inverted, that is, {overscore(C)}₂(1)=(−1,−1) and {overscore (C)}₂(2)=(−1,1), respectively. Thus,C_(2n) is defined as shown in FIG. 2.

[0128] The row vectors of the matrices generated here become Walshfunctions

[0129]FIG. 3 illustrates row vectors of matrices in a hierarchicalstructure.

[0130] The suffix to a symbol C represents the degree of the matrix. InFIG. 3, the maximum degree is 64. At the minimum transmission rate, oneof the 64 row vectors {C₆₄(1), . . . , C₆₄(64)} is generated as theorthogonal code. At the transmission rate double the minimumtransmission rate, one of the 32 row vectors {C₃₂(1), . . . , C₃₂(32)}is assigned as the orthogonal code. In assigning one of the row vectorsin the matrix of a particular degree, a row vector is selected whichdoes not include any lower hierarchical row vectors which are alreadyassigned.

[0131] In other words, when selecting one of the row vectors of2^(k)×2^(k) matrix as the orthogonal code, where k is an integer, anyrow vectors in the entire 2^(j)×2^(j) matrices, which are alreadyassigned, where j is an integer greater than k, are not included in thatrow vector to be selected or its inverted row vector, as sub-vectors.

[0132]FIG. 4 illustrates more concretely the orthogonal codes which aregenerated at respective transmission rates.

[0133] In FIG. 4, the orthogonal codes with the rate twice the maximuminformation transmission rate are illustrated in the hierarchicalstructure as in FIG. 3. In this figure, the orthogonal codes theorthogonal code generator 101 of FIG. 1 generates are shown at points A,B, C and D. Each point A indicates the orthogonal code corresponding tothe minimum transmission rate (equal to ⅛ of the maximum transmissionrate), and each point D represents the orthogonal code with atransmission rate eight times that of the minimum rate (that is, themaximum transmission rate). As illustrated in FIG. 4, the orthogonalcodes associated with the points D have two bits per unit informationlength.

[0134] The orthogonal codes as shown in FIGS. 1 and 4 are explained inconnection with the orthogonal codes with a bit rate twice the maximumtransmission rate. The bit rate of the orthogonal codes in use, however,can be 2^(n) times such as four times, eight times, etc. of the maximuminformation rate, where n is a natural number.

[0135]FIGS. 5A and 5B show examples, in which the bit rate of theorthogonal codes in use is four times the maximum transmission rate. InFIG. 5A, each point A′ represents the orthogonal code associated withthe minimum transmission rate (equal to ⅛ of the maximum transmissionrate), and each point D′ indicates the orthogonal code with a rate eighttimes that of the minimum transmission rate (that is, the maximumtransmission rate).

[0136] The orthogonal codes associated with the points D′ of FIG. 5Ahave four bits per unit information length. FIG. 5B shows anotherexample, in which the bit rate of the orthogonal codes is four times themaximum transmission rate. As shown in FIGS. 5A and 5B, the orthogonalcode can be used which is selected in a particular level of thehierarchy such that it does not include any lower level orthogonal codeslinked to the selected one in the hierarchy. For example, since thepoint E in FIG. 5B includes the lower level points A″ and B″ in use, thepoint D″ is selected which does not include those points A″ and B″.

[0137] When the CDMA signal thus transmitted is received, thetransmission rate can be decided directly from the signal. This will nowbe described with reference to FIG. 6, a block diagram showing aconfiguration of a demodulator of a receiving side. FIG. 6 shows only astage after the transmitted signal is received, converted into thebaseband, and further converted into a digital form.

[0138] In FIG. 6, the reference numeral 401 designates a multiplier fordespreading the received signal by multiplying it by the spreading codesequence fed from the spreading code sequence generator 402. Thereference numeral 403 designates a sampler that samples the output ofthe multiplier 401 at the bit rate of the orthogonal code, that is, at arate twice the maximum information transmission rate. The referencenumeral 420 designates a correlator that calculates correlations bymultiplying the despread and sampled received signal by the orthogonalcodes which are used for respective transmission rates on thetransmitting side. For example, when the transmitted signal uses theorthogonal codes as illustrated in FIG. 4, the correlations arecalculated with four orthogonal codes. The correlator 420 includes, foreach orthogonal code, a multiplier 421, an integrator 422, a squarecircuit 423 and an accumulator 424, and calculates the correlations withthe orthogonal codes by carrying out parallel operations with theorthogonal codes. The integrators 422 each integrate during unitinformation length of the corresponding information rate, and theaccumulators 424 also add at every unit information length interval. Forexample, in the orthogonal codes in FIG. 4, the addition is carried outeight times at the minimum information rate. The reference numeral 404designates a maximum value code selector that receives the results ofthe correlator 420, and selects the orthogonal code with the maximumcorrelation value.

[0139] The reference numeral 405 designates a delay for delaying thereceived signal until the maximum value code selector 404 detects theorthogonal code with the maximum correlation value. The referencenumeral 407 designates an orthogonal code generator for generating theorthogonal code selected by the maximum value code selector 404, and 406designates a multiplier that multiplies the sampled received signal bythe orthogonal code. The reference numeral 408 designates an integratorfor integrating during unit information period of the correspondinginformation rate, and 410 designates a phase demodulator fordemodulating the received signal.

[0140] In FIG. 6, the baseband digital received signal is despread bythe multiplier 401 using the spreading code sequence, followed bysampling of the despread signal by the sampler 403 at the bit rate ofthe orthogonal code (that is, double the maximum information rate). Thecorrelator 420, which has prepared the groups of the orthogonal codesused on the transmitting side, calculates the correlations with thesampled signal sequence. Then, the maximum value code selector 404compares the correlation values with each other, and makes a decisionthat the rate of the orthogonal code with the maximum correlation valueis the rate of the transmitted information.

[0141] The correlator 420 in FIG. 6 will now be described in moredetail. The sampling rate of the received signal is twice the maximuminformation rate Rmax. In the correlator 420, the orthogonal code 1corresponds to the maximum information rate, and the orthogonal codeQmax corresponds to the minimum information rate. The integrators in thecorrelation calculation block each have an integration time of unitinformation length at respective information rates corresponding to theintegrators. The square circuits 423 are each interposed to square thecorresponding correlation value. The accumulators are provided because aplurality of pieces of information appear during the unit informationinterval of the minimum information rate, when the transmission rate isother than the minimum transmission rate. For example, when the maximumrate is eight times the minimum rate, the accumulator of the orthogonalcode 1 carries out additions eight times, and the accumulator of theorthogonal code 2 carries out additions four times. Thus, thecorrelation values are compared at every unit information interval ofthe minimum rate, and the code giving the maximum value is selected,which code is indicated by the index Q′ in FIG. 6.

[0142] In the arrangement as shown in FIG. 6, the sampled sequence ofthe received signal must be delayed to compensate for the delay due tothe rate decision. The delay 405 is provided to ensure the delay.

[0143] Once the information rate has been decided, correlation iscalculated between the orthogonal code sequence corresponding to theinformation rate and the sampled sequence of the received signal, andthe sequence of the correlation values gives the received sequence.

[0144] Specifically, the orthogonal code selected by the maximum valuecode selector 404 is generated by the orthogonal code generator 407, andis multiplied with the delayed sampled sequence of the received signal,followed by the integration during the interval corresponding to thedecided information rate.

[0145] Since the received information sequence is usually phasemodulated, the correlation value sequence is phase demodulated by thephase demodulator 410 into the original data sequence. Thus, thereceiver can detect the transmission rate by calculating the correlationwith the orthogonal codes. Although the foregoing description isprovided in connection with the CDMA communication scheme, it is obviousthat the present detection method of the transmission rate can beapplied to other communication schemes based on digital transmission andreception.

[0146] In the DS-CDMA described in the foregoing embodiment, it is knownprior to the present application that pilot symbols are widely used forcommunications. The pilot symbols will now be described. The pilotsymbols of a known pattern are inserted into data symbols periodically.Using the known pilot symbols makes it possible to estimate a transferfunction of a channel, and to achieve accurate demodulation bycorrecting received data symbols. A section sandwiched by two successivesets of pilot symbols which are sent periodically is referred to as aslot. The change in the rate is carried out frame by frame, whichconsists of a plurality of slots.

[0147] In the CDMA, frequency drift correction, which is analogous tothe radio central frequency drift correction between a transmitter and areceiver, can be carried out in response to information acquired bysampling the received signal at a rate equal to or greater than aspreading code rate (chip rate). Such a processing is generallyperformed on the receiving side using the pilot symbols of a knownpattern inserted into the received signal.

[0148] In the present invention, to decide the rate which is changed ona frame by frame basis, the transmitted data is multiplied on thetransmitting side by the orthogonal code with a length corresponding tothe data rate. In this case, the entire transmitted data including thepilot symbols undergoes the rate change.

[0149] When trying to perform the drift correction or the like of such areceived signal, the signal after sampling by the sampler 403 in FIG. 6(that is, the signal sampled at the rate twice the symbol rate) cannotbe used for the frequency drift correction or the like. Accordingly, thepilot symbols to be used for the frequency drift correction or the likemust be acquired, after the rate decision result is obtained, bymultiplying the received signal before the sampling with the sampler 403in FIG. 6 by the orthogonal code corresponding to the decided rate toreturn the received signal to its original form.

[0150] To perform accurate measurement of the received SIR of theinformation symbols other than the pilot symbols, it is necessary forthe information symbols to undergo demodulation (multiplication of thesampled sequence of the received signal by the orthogonal code with themaximum correlation value) based on the rate decision (decision of theorthogonal code) at every slot interval.

[0151] To achieve the drift correction or the like after the ratedecision, the received signal must be delayed until the rate decisionresult of required accuracy is obtained, which necessitates to store thereceived signal in a memory. The memory used for this purpose, however,has a drawback that its scale becomes rather large in the CDMA receiver(this is because to store the information during the same duration, thecapacity of such a memory must be increased by a factor of theprocessing gain as compared with the capacity of a memory for storingthe sampling data at the symbol rate).

[0152] In view of this, the pilot symbols can always be transmitted at afixed symbol rate (usually, at a symbol rate equal to the maximum datarate), in which case, the transmitter side does not carry out themultiplication of the transmitted signal by the orthogonal codecorresponding to the data rate. This makes it possible.for the receivingside to carry out the frequency drift correction or the like using thatportion (pilot symbols) of the received signal before the rate decisionresult is obtained. In this case, the pilot symbols are transmitted atthe same transmission power as that applied to the slot data rate.

[0153] Transmitting the pilot symbols at the fixed rate can make therate decision of the pilot symbols unnecessary, and obviate the memoryfor storing the information at the chip rate, thereby being able toreduce the circuit scale.

[0154] In this case, since the pilot symbols are not used for the ratedecision, it is expected that the accuracy of the rate decision islowered slightly. However, its effect is considered to be very smallbecause the ratio of duration the pilot symbols occupy in thetransmitted data symbols in the frame (or in the slot) is rather small(less than {fraction (1/10)} in normal cases).

[0155] In the CDMA mobile communications, the power of the transmittedsignal must be controlled optimally according to its receiving side. Inthe variable rate transmission, since the transmission power is varieddepending on the rate, the transmission power control must be carriedout according to the rate.

[0156] Referring to FIGS. 7 and 8, a receiving scheme will now bedescribed which employs the transmission power control that controls thetransmission power such that the receiving quality is maintained atconstant by matching the received SIR (signal to interference ratio)measured on the receiving side to a target SIR, when the foregoingvariable rate transmission is carried out.

[0157]FIG. 7 is a block diagram showing a configuration of the receiver,and FIG. 8 is a diagram illustrating the processing of slots received bythe receiver with the structure as shown in FIG. 7. In FIG. 7, the samecomponents as those of the receiver as shown in FIG. 6 are designated bythe same reference numerals.

[0158] The received signal is despread using the spreading codesequence, followed by the calculation of the correlations by thecorrelator 420 using the foregoing orthogonal codes, and the selectionof the orthogonal code that gives the maximum correlation value by themaximum value code selector 404. This enables the receiving side torecognize the transmission rate, and to extract the received informationsequence by demodulating the delayed received signal using theorthogonal code as described before referring to FIG. 6.

[0159] The despread received signal is supplied to a received SIRmeasuring block 450, as well. The received SIR measuring block 450measures the SIR of the received signal at every slot interval. Acorrecting block 452 corrects the SIR measured in each slot inaccordance with the rate held in a rate decision result holder 454. Acomparator 456 compares the received SIR which is corrected by thecorrecting block 452 with a target SIR fed from a target SIR settingblock 458. The rate decision result holder 454 holds the rate obtainedby the rate decision using the slots received up to the presentinstance. Since the transmission rate varies frame by frame consistingof a plurality of slots, the rate held in the rate decision resultholder 454 is reset every time the frame is changed.

[0160] To perform accurate measurement of the received SIR of theinformation symbols other than the pilot symbols, it is necessary forthe information symbols to undergo demodulation (multiplication of thesampled sequence of the received signal by the orthogonal code with themaximum correlation value) based on the rate decision (decision of theorthogonal code) at every slot interval.

[0161] A compared result, that is, the output of the comparator 456 isreflected on a transmission power command to the transmitting side.Since the compared result is obtained for each slot as described above,the transmission power command is issued at every slot interval.

[0162] As time is elapsed, the accuracy of the rate decision result isimproved, and that at the final slot in the frame is best in average.The orthogonal code for demodulating the received information sequenceis delayed by one frame interval by the delay 405, making it possible touse the decision result in the final slot.

[0163]FIG. 8(a) illustrates the received signal when the transmission ofthe signal is switched from the transmission rate Q=1 to Q=2. Whentransmitted at the rate Q=2, the transmission power is reduce. FIG. 8(b)illustrates in an enlarged scale the final slot of the frame transmittedat the rate Q=1, and a few initial slots of the frame transmitted at therate Q=2. FIG. 8(c) illustrates the timings at which the correlation iscalculated.

[0164] Referring to FIG. 8, a processing when the frame is switched willbe described.

[0165] In FIG. 8(b), take notice of the final slot of the frame beforethe switch of the rate and the first slot of the frame immediately afterthe rate switch. As illustrated in FIG. 8(c), as the first slot begins,the correlation calculation is started. The rate is decided on the basisof the correlation calculation results, and the received SIR for thesecond slot is corrected. The correlation calculation of the second slotis continued, and the calculation results up to the end of the slot isused for correcting the target SIR of the third slot. Thus, since thesecond and following slots can carry out the comparison using thereceived SIR corrected according to the rate, accurate transmissionpower control can be achieved.

[0166] However, since the rate decision result holder 454 is reset frameby frame as described above, the first slot of the frame cannot obtainthe rate decision results. As a result, since the correction accordingto the rate cannot be achieved, the first slot cannot carry out theaccurate comparison of the received SIR.

[0167] Circumvention of this will now be described. FIG. 8(b)illustrates the case in which the pilot symbols indicated by A (that is,the initial pilot symbols of the first slot) are inserted by multiplyingit by a power coefficient corresponding to the previous rate.Accordingly, when obtaining the received SIR of the pilot symbols, thecorrection according to the rate can use the rate obtained in theprevious frame. This makes it possible to carry out the transmissionpower control by correcting the received SIR of the pilot symbols of thefirst slot, and by comparing the corrected SIR with the target SIR.

[0168] Such receiving control can be implemented by delaying the resetof the rate decision result holder 454 from the end of the frame to atime immediately before the rate decision results are obtained of thefirst slot of the next frame, and by carrying out the correction usingthe rate of the preceding frame held in the rate decision result holder454. This makes it possible to implement the transmission power controlmatching the first slot of the frame using the received SIR of the pilotsymbols, even if the transmission rate is changed from frame to frame.

[0169] Alternatively, since the accurate comparison of the received SIRcannot be expected with the first slot of the frame, the transmittingside can ignore the transmission power control command which isassociated with the first slot of the frame and is sent from thereceiving side, so as to avoid the transmission power control based onthat transmission power control command. In this case, it is notnecessary to assign the transmission power of the previous frame to thepilot symbols of the first slot in the frame as denoted by An of FIG.8(b).

[0170] The negligence of the transmission power control command need notbe limited to that of the first slot. For example, it is possible tosuspend the transmission power control in initial slots (the firstseveral slots of the frame), where the rate decision accuracy is ratherlow within the frame (that is, it is unlikely that the correction of theSIR measured values based on the decision rate can be carried outaccurately), and to restart the transmission power control from the slotwith which it becomes possible to make the rate decision at considerableaccuracy. In this case, the slot number from which the transmissionpower is restarted is determined considering the final transmissionquality (such as the average bit error rate).

[0171] In measuring the SIR of the received signal, it is possible tomeasure the received SIR of the pilot symbols that are transmitted atthe fixed rate.

[0172] In the foregoing embodiment, the description is provided inconnection with the configuration which corrects the received SIR fromthe received SIR measuring block 450 according to the transmission rate,as shown in FIG. 7. Since the configuration corrects the variations inthe received SIR in response to the transmission rate, a conventionaltransmission power control system based on the received SIR andemploying an invariable transmission rate can be applied with outchange.

[0173] As an alternative of FIG. 7, other configurations can beimplemented which compare the received SIR with the target SIR. Forexample, an arrangement is possible which corrects the target SIR inaccordance with the transmission rate.

[0174] Another embodiment will now be described for circumventing theforegoing problem. As described before, when the pilot symbols aretransmitted intermittently at the fixed rate, it is not necessary withthe pilot symbols to make the rate decision or to correct the receivedSIR as long as the transmission power of the pilot symbols is not variedin response to the rate. Therefore, as long as the received SIR ismeasured using the pilot symbols transmitted at the fixed rate, thetransmission power control can be achieved by comparing the received SIRof the pilot symbols with the target SIR without correcting thatreceived SIR. In this case, the system for correcting the received SIRcan be omitted.

[0175] As described above, the present invention can detect the rate onthe receiving side without the information indicating the transmissionrate.

[0176] In addition, the signal transmitted at the variable rate canundergo accurate transmission power control using the foregoingtransmission power control.

What is claimed is:
 1. A variable rate transmission method comprisingthe steps of: selecting, in accordance with a rate of information to betransmitted, one of a plurality of orthogonal codes whose length differsfrom each other and whose information rate is at least twice a maximuminformation rate; and multiplying a transmitted signal by the selectedorthogonal code.
 2. The variable rate transmission method as claimed inclaim 1, wherein said orthogonal code is obtained by successivelygenerating, using lower degree matrices under a predetermined rule,higher degree (2^(N)×2^(N) elements, where N is an integer equal to orgreater than one) matrices with their row vectors orthogonal to eachother, and by selecting one of row vectors of one of said matrices witha degree varying in accordance with a peak transmission rate oftransmitted data.
 3. The variable rate transmission method as claimed inclaim 2, wherein said orthogonal code is selected, when selecting one ofrow vectors of a 2^(k)×2^(k) element matrix, where k is an integer lessthan N, such that any of row vectors which belong to any one of2^(j)×2^(j) element matrices, where j is an integer greater than k, andwhich are already assigned as the orthogonal codes, do not include astheir sub-vector, a row vector to be selected and a row vector obtainedby inverting the row vector to be selected.
 4. The variable ratetransmission method as claimed in any one of claims 1-3, wherein saidtransmitted signal is further multiplied by a spreading code sequence tobe spectrum spread, and is transmitted at transmission powercorresponding to said rate.
 5. The variable rate transmission method asclaimed in claim 4, further comprising the steps of: inserting pilotsymbols of a known pattern periodically into data symbols correspondingto said information to be transmitted; and varying the rate on a frameby frame basis, said frame consisting of a plurality of slots defined bysaid pilot symbols.
 6. The variable rate transmission method as claimedin claim 5, further comprising the step of controlling the transmissionpower on a slot by slot basis in response to a transmission powercontrol command sent from a receiving side.
 7. The variable ratetransmission method as claimed in claim 6, further comprising the stepof transmitting, in a slot immediately after a rate change, the pilotsymbols at power corresponding to the rate before the rate change. 8.The variable rate transmission method as claimed in claim 6, furthercomprising the step of suspending the transmission power control by saidtransmission power control command that is associated with at least oneof slots immediately after a rate change.
 9. The variable ratetransmission method as claimed in claim 8, wherein a number of slotswith which said transmission power control is suspended is determined inresponse to transmission quality.
 10. The variable rate transmissionmethod as claimed in any one of claims 6-8, where said pilot symbols aretransmitted at a same rate as that of said frame.
 11. The variable ratetransmission method as claimed in any one of claims 6-8, where saidpilot symbols are transmitted at a fixed rate.
 12. A variable ratereceiving method for receiving a signal transmitted by the variable ratetransmission method as claimed in any one of claims 1-5, said receivingmethod comprising the steps of: generating a sampled sequence of areceived signal by sampling the received signal at a rate of one of theorthogonal codes, and calculating correlations between the sampledsequence of the received signal and the plurality of orthogonal codeswith different lengths; deciding an orthogonal code that gives a maximumcorrelation by comparing correlation values obtained as a result of thecalculation of the correlations; and demodulating the received signal bymultiplying the sampled sequence of the received signal by theorthogonal code that gives the maximum correlation value.
 13. Areceiving method for receiving a signal transmitted by the variable ratetransmission method as claimed in any one of claims 6-8, said receivingmethod comprising the steps of: generating a sampled sequence of areceived signal by sampling the received signal at a rate of one of theorthogonal codes; calculating correlations between the sampled sequenceof the received signal and the plurality of orthogonal codes withdifferent lengths; deciding an orthogonal code that gives a maximumcorrelation by comparing correlation values obtained as a result of thecalculation of the correlations; demodulating the received signal bymultiplying the sampled sequence of the received signal by theorthogonal code that gives the maximum correlation value, and measuringa received SIR for each slot of the received signal; correcting thereceived SIR according to a rate of the orthogonal code decided by thestep of deciding; comparing the corrected received SIR with a targetSIR; and generating a transmission power control command in response toa result of said comparing.
 14. The receiving method as claimed in claim13, wherein demodulation of said received signal is carried out slot byslot.
 15. A receiving method for receiving a signal transmitted by thevariable rate transmission method as claimed in claim 7, said receivingmethod comprising the steps of: generating a sampled sequence of areceived signal by sampling the received signal at a rate of one of theorthogonal codes; calculating correlations between the sampled sequenceof the received signal and the plurality of orthogonal codes withdifferent lengths; deciding an orthogonal code that gives a maximumcorrelation by comparing correlation values obtained as a result of thecalculation of the correlations; demodulating the received signal bymultiplying the sampled sequence of the received signal by theorthogonal code that gives the maximum correlation value; measuring areceived SIR of said pilot symbols for a slot immediately after a ratechange, and a received SIR for each of other slots; correcting thereceived SIR for each of other slots according to a rate decided by thedecision of the orthogonal code; correcting the received SIR of thepilot symbols according to a rate before the rate change; comparing thecorrected received SIR with a target SIR; and generating a transmissionpower control command in response to a result of said comparing.
 16. Areceiving method for receiving a signal transmitted by the variable ratetransmission method as claimed in claim 9, said receiving methodcomprising the steps of: generating a sampled sequence of a receivedsignal by sampling the received signal at a rate of one of theorthogonal codes; calculating correlations between the sampled sequenceof the received signal and the plurality of orthogonal codes withdifferent lengths; deciding an orthogonal code that gives a maximumcorrelation by comparing correlation values obtained as a result of thecalculation of the correlations; demodulating the received signal bymultiplying the sampled sequence of the received signal by theorthogonal code that gives the maximum correlation value; measuring areceived SIR of said pilot symbols at the fixed rate; correcting thereceived SIR according to a rate decided by the decision of theorthogonal code; comparing the corrected received SIR with a target SIR;and generating a transmission power control command in response to aresult of said comparing.
 17. A variable rate transmitter comprising: anorthogonal code generator for generating, in accordance with a rate ofinformation to be transmitted, one of a plurality of orthogonal codeswhose length differs from each other and whose information rate is atleast twice a maximum information rate; and a multiplier for multiplyinga transmitted signal by the orthogonal code fed from said orthogonalcode generator.
 18. The variable rate transmitter as claimed in claim17, wherein said orthogonal code is obtained by successively generating,using lower degree matrices under a predetermined rule, higher degree(2^(N)×2^(N) elements, where N is an integer equal to or greater thanone) matrices with their row vectors orthogonal to each other, and byselecting one of row vectors of one of said matrices with a degreevarying in accordance with a peak transmission rate of transmitted data.19. The variable rate transmitter as claimed in claim 18, wherein saidorthogonal code is selected, when selecting one of row vectors of a2^(k)×2^(k) element matrix, where k is an integer less than N, such thatany of row vectors which belong to any one of 2^(j)×2^(j) elementmatrices, where j is an integer greater than k, and which are alreadyassigned as the orthogonal codes, do not include as their sub-vector, arow vector to be selected and a row vector obtained by inverting the rowvector to be selected.
 20. The variable rate transmitter as claimed inany one of claims 17-19, further comprising: a spreading sequencegenerator for generating a spreading code sequence for spectrumspreading; a multiplier for multiplying the transmitted signal by thespreading code sequence fed from said spreading sequence generator; anda transmitter for varying transmission power in response to thetransmission rate.
 21. The variable rate transmitter as claimed in claim20, further comprising a pilot symbol generator for generating pilotsymbols of a known pattern periodically, wherein said pilot symbols areinserted into data symbols corresponding to said information to betransmitted, and the rate is varied on a frame by frame basis, saidframe consisting of a plurality of slots defined by said pilot symbols.22. The variable rate transmitter as claimed in claim 21, furthercomprising a transmission power controller for controlling thetransmission power on a slot by slot basis in response to a transmissionpower control command sent from a receiving side.
 23. The variable ratetransmitter as claimed in claim 22, wherein said pilot symbols aretransmitted, in a slot immediately after a rate change, at powercorresponding to the rate before the rate change.
 24. The variable ratetransmitter as claimed in claim 21, where said pilot symbols aretransmitted at a same rate as that of said frame.
 25. The variable ratetransmitter as claimed in claim 21, where said pilot symbols aretransmitted at a fixed rate.
 26. The variable rate transmitter asclaimed in claim 22, wherein the transmission power control by saidtransmission power control command that is associated with at least oneof slots immediately after a rate change is suspended.
 27. The variablerate transmitter as claimed in claim 26, wherein a number of slots withwhich said transmission power control is suspended is determined inresponse to transmission quality.
 28. A variable rate receiver forreceiving a signal transmitted by the variable rate transmission methodas claimed in any one of claims 1-5, said receiver comprising: a samplerfor generating a sampled sequence of a received signal by sampling thereceived signal at a rate of one of the orthogonal codes; a correlatorfor calculating correlations between the sampled sequence of thereceived signal from said sampler and the plurality of orthogonal codeswith different lengths; an orthogonal code decision block for decidingan orthogonal code that gives a maximum correlation by comparingcorrelation values obtained as a result of the calculation of thecorrelations; an orthogonal code generator for generating the orthogonalcode decided by said orthogonal code decision block; and a multiplierfor multiplying the sampled sequence of the received signal by theorthogonal code from said orthogonal code generator to demodulate thereceived signal.
 29. A receiver for receiving a signal transmitted bythe variable rate transmission method as claimed in any one of claims6-8, said receiver comprising: a sampler for generating a sampledsequence of a received signal by sampling the received signal at a rateof one of the orthogonal codes; a correlator for calculatingcorrelations between the sampled sequence of the received signal and theplurality of orthogonal codes with different lengths; an orthogonal codedecision block for deciding an orthogonal code that gives a maximumcorrelation by comparing correlation values obtained as a result of thecalculation of the correlations; an orthogonal code generator forgenerating the orthogonal code decided by said orthogonal code decisionblock; a multiplier for multiplying the sampled sequence of the receivedsignal by the orthogonal code from said orthogonal code generator; areceived SIR for measuring a received SIR for each slot of the receivedsignal; a correcting block for correcting the received SIR according toa rate of the orthogonal code decided; and a comparator for comparingthe corrected received SIR with a target SIR, wherein a transmissionpower control command is generated in response to a result of saidcomparing.
 30. The receiver as claimed in claim 29, wherein demodulationof said received signal is carried out slot by slot.
 31. A receiver forreceiving a signal transmitted by the variable rate transmission methodas claimed in claim 7, said receiver comprising: a sampler forgenerating a sampled sequence of a received signal by sampling thereceived signal at a rate of one of the orthogonal codes; a correlatorfor calculating correlations between the sampled sequence of thereceived signal from said sampler and the plurality of orthogonal codeswith different lengths; an orthogonal code decision block for decidingan orthogonal code that gives a maximum correlation by comparingcorrelation values obtained as a result of the calculation of thecorrelations; an orthogonal code generator for generating the orthogonalcode decided by said orthogonal code decision block; a multiplier formultiplying the sampled sequence of the received signal by theorthogonal code from said orthogonal code generator; a received SIRmeasuring block for measuring a received SIR of said pilot symbols for aslot immediately after a rate change, and a received SIR for each ofother slots; a correcting block for correcting the received SIR for eachof other slots according to a rate decided by the decision of theorthogonal code, and for correcting the received SIR of the pilotsymbols according to a rate before the rate change; and a comparator forcomparing the corrected received SIR with a target SIR, wherein atransmission power control command is generated in response to a resultof said comparing.
 32. A receiver for receiving a signal transmitted bythe variable rate transmission method as claimed in claim 11, saidreceiver comprising: a sampler for generating a sampled sequence of areceived signal by sampling the received signal at a rate of one of theorthogonal codes; a correlator for calculating correlations between thesampled sequence of the received signal and the plurality of orthogonalcodes with different lengths; an orthogonal code decision block fordeciding an orthogonal code that gives a maximum correlation bycomparing correlation values obtained as a result of the calculation ofthe correlations; a multiplier for multiplying the sampled sequence ofthe received signal by the orthogonal code that gives the maximumcorrelation value; a received SIR measuring block for measuring areceived SIR of said pilot symbols at the fixed rate; a correcting blockfor correcting the received SIR according to a rate decided by thedecision of the orthogonal code; and a comparator for comparing thecorrected received SIR with a target SIR, wherein a transmission powercontrol command is generated in response to a result of said comparing.